The regulation of the proliferation of human prostate cells is not well understood. Androgens control the number of prostate cells by inducing cell proliferation, inhibiting cell death and by inhibiting cell proliferation (shutoff). It has been postulated that defects in the shutoff mechanism are probably responsible for tumor development is aging human populations. The main objective of this research is to understand the mechanism by which physiological androgen levels inhibit the proliferation of their target cells in adult and aging men. Human prostate carcinoma LNCaP-FGC cells lost the ability to undergo programmed cell death upon androgen withdrawal; they were chosen as a model to study androgen control of cell proliferation because they respond to androgens biphasically, in a dose-dependent manner (increased cell proliferation at low doses; proliferation inhibition at high doses). Variants LNCaP-TAC and LNCaP-LNO will be used to unravel these effects because the former expresses only the proliferative response to androgens whereas the latter expresses only the inhibitory effect. During the first cycle of funding we have isolated differentially expressed sequences that are candidates for mediators of the shutoff response. Specific Aims are: 1) To assess the biological role of the candidate sequences by specifically blocking the expression of the peptide they encode by means of antisense oligonucleotides. 2) To assess the biological role of these candidate sequences by stable transfection of expression vectors containing the candidate full length encoding sequences. Expression of candidate shutoff sequences will be tested using the tetracycline- controlled gene expression system. 3) The relevance of these sequences on tumor growth will be assessed by studying the growth pattern of cloned stable transfectants inoculated into nude mice. Three hypotheses will be explored: a) androgens trigger a proliferative shutoff by inducing a 'master gene' which will in turn regulate other genes involved in the process, b) androgens directly control several genes that act simultaneously to induce the shutoff phenotype and c) a combination of a and b. The realization of this proposal will make possible to develop l) tools to recognize the presence of this cell phenotype, ll) therapeutic strategies to I) control the proliferation of these cell, and ii) select against the appearance of hormone-resistant phenotypes during progression. This knowledge may also provide a better understanding of mechanisms underlying the malignant transformation of the prostate.